Why does Adobe require that I install Express Photo just to open a PDF in Acrobat Reader I downloaded from my healthcare system?

When I attempted to download a medical document from my healthcare provider/hospital system, before I could see the document, a box popped up that required that I download and install Adobe Photo Express. There was no option to decline or do it later. This was a forced install. The tab was frozen. The only actionable item was the Install App button. The format made it look like this mandate to download and install Adobe Photo Express was a requirement of the “My Chart” medical records web page as it overlaid my”My Chart” web page. 
When I was done downloading and installing Express Photo, it asked if I wanted to continue to open the document. I clicked YES and my document opened in Acrobat Reader, not Photo Express.